The present invention relates to seals in a gas turbine for supplementing the chordal hinge seals between turbine nozzles and a turbine nozzle support ring and particularly relates to supplementary seals for substantially minimizing or eliminating leakage losses past the chordal hinge seals.
In a gas turbine, hot gases of combustion flow from combustors through first-stage nozzles and buckets and through the nozzles and buckets of follow-on turbine stages. The first-stage nozzles typically include an annular array or assemblage of cast nozzle segments each containing one or more nozzle stator vanes per segment. Each first-stage nozzle segment also includes inner and outer band portions spaced radially from one another. Upon assembly of the nozzle segments, the stator vanes are circumferentially spaced from one another to form an annular array thereof between annular inner and outer bands. A nozzle retaining ring coupled to the outer band of the first-stage nozzles supports the first-stage nozzles in the gas flow path of the turbine. An annular nozzle support ring, preferably split at a horizontal midline, is engaged by the inner band and supports the first-stage nozzles against axial movement.
In an exemplary arrangement, eighteen cast segments are provided with two vanes per segment. The annular array of segments are sealed one to the other along adjoining circumferential edges by side seals. The side seals seal between a high pressure region radially inwardly of the inner band, i.e., compressor discharge air at high pressure, and the hot gases of combustion in the hot gas flow path which are at a lower pressure.
Chordal hinge seals are used to seal between the inner band of the first-stage nozzles and an axially facing surface of the nozzle support ring. Each chordal hinge seal includes an axial projection which extends linearly along a chord line of the inner band portion of each nozzle segment. Particularly, the chordal hinge seal extends along an inner rail of each segment and which rail extends radially inwardly of the inner band portion. The chordal hinge seal projection lies in sealing engagement with the axially opposite facing sealing surface of the nozzle support ring.
During operation and/or repair of the first-stage nozzle, it has been found that warpage can leave gaps between the chordal hinge seals and the sealing surface of the nozzle support ring. These gaps enable leakage past the chordal hinge seals from the high pressure area radially within the annular inner band into the hot gas flow path. That is, the chordal hinge seals are inadequate to prevent leakage flow as the chordal hinge seal projections lose contact with the sealing surface of the nozzle support ring. Consequently, there is a need for a supplemental seal at the interface of the first-stage nozzles and nozzle support ring to minimize or eliminate the leakage flow past the chordal hinge seals.
In accordance with a preferred embodiment of the present invention, there is provided a supplemental seal between the first-stage nozzles and the nozzle support ring which eliminates or minimizes leakage past the chordal hinge seals and which is readily and easily installed without reconfiguration of the first-stage nozzles or nozzle support ring. The supplemental seal comprises a generally V-shaped seal for disposition between the axially facing first surface of the nozzle support ring and an axially facing second surface of a turbine nozzle segment. Particularly, the nozzle segment includes a radially inwardly projecting inner rail mounting the chordal seal which engages the first surface of the nozzle support ring. The inner rail also has a shallow recess radially outwardly of the projection forming the chordal hinge seal. The supplemental seal is disposed between the first and second axially registering surfaces for sealing engagement therebetween.
More particularly, the supplemental seal extends arcuately between the first and second sealing surfaces and includes a stem enabling the supplemental seal to be secured to the sealing surface of the inner rail, for example, by bolting. The V-shaped portion of the supplemental seal faces inwardly and in operation, a free edge of the V-shaped seal bears against the first sealing surface. The opposite edge is joined to an edge of the stem and forms a sealing surface with the second annular surface. Thus, the V-shape opens radially inwardly in registration with the high pressure region in the event of leakage past the chordal hinge seal. Any high pressure leakage flexes or biases the seal into engagement to seal between the opposite first and second annular surfaces. The circumferential extent of the supplemental seal is preferably coincident with the circumferential extent of the nozzle segment.
A feature of the present invention resides in initially compressing and maintaining the seal compressed in a substantially arcuate planar form prior to assembly and upon initial assembly, into the machine. To accomplish this, the legs of the V-shaped seal are compressed against the stem and a material, preferably a solder, is applied to maintain the V-shaped seal in a compressed condition. The soldered compressed seal forms essentially a solid block or seal piece which facilitates handling, avoids exposed sharp edges and affords a sturdiness and robustness to the seal during handling and installation. The supplemental seal is installed by bolting in its compressed condition to the second annular surface along the shallow recess of the inner rail. When the turbine is brought up to operating conditions, e.g., when the turbine temperature exceeds that of the melting temperature of the solder, the solder melts away, releasing the V-shaped portion of the seal from its compressed state into an expanded state and into engagement with the opposite first and second sealing surfaces of the nozzle support ring and the inner rail, respectively.
In a preferred embodiment according to the present invention, there is provided a turbine comprising a turbine nozzle support ring having a generally axially facing first surface, a turbine nozzle segment having at least one stator vane and including an inner band having a second surface in axial opposition to the first surface, a flexible seal between the first and second surfaces including a seal body between high and low pressure regions on opposite sides of the seal, the seal body including first and second portions in opposition to one another and coupled to one another along adjoining edges thereof, opposite edges of the first and second portions being spaced from one another defining an opening into a cavity in the seal body between the first and second portions, the first and second portions being preloaded to bear against the first and second surfaces, respectively, with the cavity opening toward the high pressure region.
In a further preferred embodiment according to the present invention, there is provided a gas turbine comprising a turbine nozzle support ring having a generally axially facing first surface, a turbine nozzle segment having at least one stator vane and including an inner band having a second surface in axial opposition to the first surface, a flexible seal between the first and second surfaces including a seal body between high and low pressure regions on opposite sides of the seal, the seal body including first and second portions in opposition to one another and coupled to one another along adjoining edges thereof, the seal body including a stem extending from the second seal portion and bearing against one of the first and second surfaces, an overlay of material along at least the first and second portions and at least portions of the stem maintaining the first and second portions in a state of compression generally against the stem portion, the material being releasable from the portions to enable the first and second portions to resiliently move away from one another and from the stem to engage a distal edge of the first portion against another of the first and second surfaces, respectively.
In a further preferred embodiment according to the present invention, there is provided a method of forming a seal in a gas turbine having a nozzle support ring including a first axially facing sealing surface and an annular array of nozzles formed of a plurality of nozzle segments each having an inner band and a second, generally axially facing sealing surface in general axial opposition to the first surface comprising the steps of providing a flexible seal having first and second portions in opposition to one another and connected to one another along adjoining edges thereof, compressing the first and second portions toward one another to form a compressed seal, securing the compressed seal to one of the first and second surfaces and between the surfaces and releasing the first and second portions of the compressed seal to enable a distal edge of the first portion remote from the adjoining edges to engage another of the first and second surfaces.